A cement mortar for extrusion molding includes a cement, a fine aggregate, a fiber, and an additive. In general, the cement mortar for extrusion molding has been used in the fields of civil engineering and construction such as exterior wall materials, roofing materials, flooring materials, and soundproof wall materials for construction.
Asbestos, which has been conventionally used as the fiber, decreases discharge pressure of a cement mortar during extrusion molding, increases surface smoothness of extrusion-molded products, and decreases green body hardness of the extrusion-molded products, and thus cement extrusion-molded products have been manufactured with high molding efficiency. However, since asbestos has been designated as a carcinogenic material, the use of asbestos in the cement mortar for extrusion molding has been strictly restricted by the law. Thus, various fibers such as inorganic fiber such as glass fiber, pulp such as carbon fiber, wastepaper, polyamide fiber, polypropylene fiber, and polyester fiber have replaced asbestos in cement mortar for extrusion molding. Although pulp or wastepaper has been mainly used to replace asbestos, the use of pulp or wastepaper having lower strength and dispersibility than asbestos may cause problems such as decrease in discharge pressure of cement mortar during extrusion molding, hardness of extrusion-molded products, surface smoothness of the extrusion-molded products, and/or molding efficiency of the extrusion-molded products.
In order to overcome these problems, cellulose derivatives such as cellulose ether have been widely used as cement mortar additives for extrusion molding. This is because the cellulose derivatives increase plasticity, water retentivity, and lubricity of the cement mortar for extrusion molding, thereby providing higher molding efficiency of the extrusion-molded products.
Hydroxypropylmethylcellulose (HPMC) and hydroxyethylmethylcellulose (NEMC) have been used as the cellulose derivatives. Intrinsic physical properties of the cellulose derivatives may vary according to types of substituent, degree of substitution, and pattern of substitution, and physical properties of extrusion molded panels may also be influenced thereby.
Water retentivity and lubricity of extrusion-molded products may be improved to a predetermined level by using currently available cellulose derivatives. However, to further improve quality of extrusion-molded products and productivity thereof, there is a need to improve workability of cement mortar for extrusion molding and increase productivity of extrusion-molded products by increasing water retentivity and lubricity of the extrusion-molded products and reducing discharge pressure of the cement mortar for extrusion molding and to enhance dimensional stability of the extrusion-molded products such as a cement panel. However, these properties cannot be obtained simply by increasing the amount of the cement mortar additive for extrusion molding, and there is a need to find a fundamental solution.